Energon cube

This is the safest form of energon, used for transportation and storage.

Fiction

G1 Animated Series

NRG

As originally introduced, energon cubes seemed as though they could only be created by Soundwave More Than Meets The Eye, Part 1, who generated the empty cube framework from his similarly-shaped chest, but later, several other Decepticons proved able to produce them as well. It seemed as if energon cubes were a recent Decepticon invention -- precisely when they were concieved is unclear -- as the Autobots were apparently unaware of them until their reawakening on Earth in 1984, when Hound described them to Prime as simply "some kind of cube". By 2005, however, the Autobots had begun to use energon cubes for power as well.

Exactly how an energon cube operates is unclear, especially as their framework appears to be some sort of self-sustaining force field with no internal mechanisms. Most frequently, the empty cube is simply attached to or placed near the energy source from which it is to drain power, and the energy in question is automatically converted into liquid energon that fills the cube. Energon cubes have proven able to transform a vast array of resources into energon, including electricity, magma, oil and steam. The liquid energon within energon cubes is a glowing pink color, although the cubes could also be compressed for easy storage and transport, causing them to take on an irridescent rainbow effect.

Beast Wars

In Beast Wars, the naturally-occuring energon on prehistoric Earth appeared only in an unstable raw crystalline form. However, after the Planet Buster baked Earth's surface, the crystals were all either incinerated or somehow "converted" into more stabe cubes. These cubes no longer emitted the dangerous radiation which prompted the Beast Warriors to adopt their beast modes in the first place. They were significantly smaller than G1 cubes and colored blue rather than pink. Rather than some sort of force field containing liquid energon, these smaller cubes may have simply been a different configuration of energon crystal, much as substances like salt can exist as cubical grains but can also grow into more traditional crystalline forms. One energon cube, in particular, was used by Blackarachnia to theaten Tarantulas to remove the mind-link he had with her, or she would detonate the cube near her head, which would also get Tarantulas as well due to their shared minds. He did so remove the link as Blackarachnia wanted. Tangled Web

Toy

Rubix, the Amazing Cube!

Energon Cubes were available with Takara's "TF Collection" reissue of the Insecticons, and the set's redeco, the Collector's Edition Insectron Clone Army (Shothole, Salvo and Zaptrap) box set released in Japan in 2004.

There were also "energon cube" accessories available with the fast-food kids meal premiums in European McDonald's restaraunts. These cubes were little more than a cheap, battery powered gimmick (the battery couldn't be replaced; the triangle-headed screws used by McD's are notoriously impossible to remove) that would make sound or light the toy up. The cubes were interchangable, but not all of them were "compatible," so to speak - Unicron's light-up feature didn't work on the more opaque plastic of the other toys.

From Teletraan I: The Transformers Wiki, a Wikia wiki.